An update and good news...
HarryP - I did as you wrote and ran NPE.exe under safe mode. But before I did that I created another administrator user and used that user to run the program. It reported that there were NO threats.
I had used a windows XP computer to download both NPE.exe and 20120224-002-v5i32.exe and put them on a usb memory stick. I copied both of these to the desktop of the new user.
On a whim, whilst still in safe mode, I also ran 20120224-002-v5i32.exe - AMAZING, it ran without error and said that it had found a valid Norton product and updated it.
So, next I used an md5 summer to get the signatures. First the one downloaded with the windows XP machine (which is the one that I had downloaded on a windows XP machine and which succeeded:
41961190b40eb517efcccc0a0a50cf7e *20120224-002-v5i32.exe
Then two that were downloaded by Firefox and IE on the windows 7 computer:
d84affd55a51c99dfa715434b83c49d3 *20120224-002-v5i32.exe
abcab0c2b3a36532e64cf19011247356 *20120224-002-v5i32(1).exe
AAAARRGGGHH - all different!!!
I then switched back to the original (administrator) user in full Windows and ran the Liveupdater. This downloaded around 70 megabytes and installed 2 updates successfully. This is the first time the automatic update has run without error on version 6 on this Windows 7 computer. I then rebooted and re-ran liveupdate which told me my product was fully up to date.
So, the immediate problem has been fixed, but it looks like I have a problem with downloading files. I have previously been caught out by anti-virus programs screwing up large downloads which are done by a downloader in parts with the AV intercepting the parts and somehow interfering with their assembly. It might be that. I will do a few more experiments before stopping this.
But in summary the original problem has now "gone away" but I don't believe has been fixed.
